MESH Types: The Most used but Least Discussed Topic in our Residency

2012-01-17T22:15:00.000-08:00

Introduction

PreOp:

Many surgeons would not operate without:

- control of glucose levels if the patient has diabetes mellitus

- smoking cessation (critical in cases of complex abdominal wall reconstructions)

- weight loss (BMI) less than 35

Main concepts are:

Pore size: Porosity is the main determinant of tissue reaction. Pores must be more than 75 μm in order to allow infiltration by macrophages, fibroblasts, blood vessels and collagen. Meshes with larger pores allow increased soft tissue in-growth and are more flexible because of the avoidance of granuloma.

Weight: The weight of the mesh depends on both the weight of the polymer and the amount of material used (pore size).

Reaction: The foreign body reaction is fairly uniform regardless of the type of foreign material, but the extent of the reaction is affected by the amount of material present. Thus pore size is once again the determining factor for meshes. As described above, meshes with small pores develop stiff scar plates which are avoided in meshes with larger pores where there is a gap between the granulomas.

Shrinkage: Shrinkage occurs due to contraction of the scar tissue formed around the mesh. Scar tissue shrinks to about 60% of the former surface area of the wound. The smaller pores of heavy weight meshes lead to more shrinkage due to the formation of a scar plate.

Infection Rate: Mesh infection is feared because it is difficult to eradicate without removing the mesh and can become clinically apparent many years after implantation. Mesh infection remains about 0.1–3%, although this is obviously higher in the infected fields, for example, in parastomal hernia repair.

Although widely practiced, there is no evidence that routine prophylaxis with antibiotics confers any protection against infection. In contrast there is some evidence that the infection risk can be lowered by impregnating meshes with antiseptics.

The risk of infection is mainly determined by the type of filament used and pore size. Microporous meshes (for example, ePTFE) are at higher risk of infection because macrophages and neutrophils are unable to enter small pores (< 10 μm). This allows bacteria (< 1 μm) to survive unchallenged within the pores. A similar problem applies to multifilament meshes.

(Message to take home)

The meshes at lowest risk of infection are, therefore, those made with monofilament and containing larger pores and eradication of infection in such meshes can be achieved without their removal.

Adhesion risk:

More with synthetic other than PTFE therefore use of composite meshes "two layers" are less recommended to reduce adherence. Biological are by far the least adherence but what you gain in adherence you lose with recurrence rate.

Types

Synthetic Meshes

With synthetic mesh, there is a lower risk for recurrence but associated with a potentially higher infection rate

-Polyglactin: (vicryl) Absorbable small pore medium wt, used in infected fields

-Polyglycolic: (Dexon) Absorbable Medium

-Polyester. PET: Non absorbable, large pores, medium wt, direct contact with the viscera has been linked with high rates of fistulas and infections, has THE WORST complications (infection , recurrence and fistulas)...sorry couldn't find a nice picture.

-Polypropylene. (Marlex, Prolene) nonabsorbable, small pore, heavy, can lead to adhesions, fistula formation, and erosion, but low infection rate

-PTFE (Gortex) Very small pores, high recurrence rates because of their low tensile strength and because they do not incorporate into the tissue, provide a protective layer to prevent adherence of the intraperitoneal contents to the prosthetic material... higher risk of infection

Composite Meshes "good for underlay"

- (composix) a layer of polypropylene mesh with a layer of nonabsorbable ePTFE, reduces adhesion

- temporary composite with an absorbable material, "collagen layer" (Parietex) nonabsorbable,lt wt, reducing adhesion

Biologic Meshes

Based on available evidence, a biologic mesh may be more appropriate in a patient with a contaminated or infected site; however, potentially there can be a higher recurrence rate.

Recurrences are less with porcine > fetal bovine tissues (heterografts) > human dermal tissue (allograft). Typical sources include porcine small intestine, porcine dermis, and bovine pericardium allowing for neovascularization, beneficial in contaminated or infected surgical fields

- Porcine submucosa (surgisis) less wound infection, and no mesh-related complications or recurrent hernias can be used in contaminated wounds

- Porcine dermis same, if perforated less serroma

- human dermis (alloderm)

Types of repair

- inlay repair, which is secured only to the fascial edges, would lead to unacceptably high risk for recurrence and no longer accepted

- Onlay, placement of mesh on top of fascia and fastened to it. Those supporting the onlay technique point to the ease of graft placement, and the ability to secure it to the edges. On the other hand, criticisms of the onlay technique include the large and expensive grafts that are necessary to achieve adequate coverage, and the fact that the graft is placed in the subcutaneous, which greatly increases the risk for potential exposure following wound infection and in ventral incisional hernia repair

- Underlay (placed below the fascia) position has been found to be effective with a low recurrence rate and is "the standard procedure for all types of ventral hernias of the midline"

Post op

The author's recommendations include keeping the patient intubated if the peak airway pressure increases over 10 cm H₂O after closing the fascia, and not closing the fascia in patients with hemodynamic instability

If synthetic mesh was used, surgical drains are removed as quickly as possible. On the other hand, if biologic mesh was used, the drains may be left in for up to 2 weeks because these meshes are not porous so there is concern about the potential for fluid accumulation

lifting restriction of 20 pounds for 3-6 months is recommended.

References:

- Which mesh for hernia repair? CN BROWN, Ann R Coll Surg Engl 2010

- pictures were obtained from google search without any copyright from any of these companies as their cheap websites have no images of their products

- ACS website for the repair type picture "not found in the new edition"

- And the main reasons I composed this are a couple of unanswerable stupid FRCS board mcqs and the medscape online CME I read :

Optimizing Mesh Usage in Complex Hernia

Michael J. Rosen

http://www.medscape.org/viewarticle/712906

Tips4Surgery

MESH Types: The Most used but Least Discussed Topic in our Residency